When a client (web browser) initiates web access, a transmission control protocol/internet protocol (TCP/IP) connection is established between the client and the web server, as shown in FIG. 1. The connection is established utilising what is known as a three-way handshake. Firstly, the client sends a SYN (synchronise idle character) signal to the server, which in turn sends a SYN signal back to the client. The client then sends an acknowledgement signal to the server, thereby acknowledging receipt of the server's SYN signal and connection is complete.
Once a connection has been established between the client and the server, the client sends a hyper text mark-up language (HTML) request to the server. Such a request may be sent as a single TCP message or may be split into two such messages. The connection is characterised by what is termed a slow start mechanism. The client sends a single HTML request, awaits a response from the server, typically including the requested data, and sends an acknowledgement to the server. After transmission of the acknowledgement, multiple data signals are received from the server, such receipt is facilitated by the client. Once all data is received, the server sends a finish signal. A finish acknowledgement signal is sent from the client to the server, and then a finish signal.
The downloading of a web page involves several TCP/IP connection establishment and tear down sequences. This is because, if the web page to be downloaded comprises more than one inline image, a separate TCP session is required for the transfer of each image from the server to the client. FIG. 1 illustrates this problem, whereby once the finished signal 102 has been transmitted by the client, the client parses (checks) the downloaded page to see if more data is required. For the example of FIG. 1, an image requires downloading, so the above detailed connection establishment and tear down sequence is run again. In this instance, there is only a single data element which is less than 1 radio link control (RLC) packet to be sent, thus the server sends a single data signal followed by a finish signal. In this instance, the slow start mechanism is not invoked.
It is thus clear that, in order to download a web page containing a plurality of images, a number of TCP connections must be made between a client and a server. This is undesirable in terms of the time overhead for the overall download of a web page.
There exists a problem in accessing the worldwide web (WWW) using sessions or applications protocols which use successive TCP connections within a session on TDMA wireless packet data systems or wireline modem access protocols. This is illustrated hereinafter with reference to the use of hyper text transfer protocol (HTTP) on a global packet radio system (GPRS). When a browser sends an HTTP request, the request is transmitted as a SYN signal. However, every time a SYN signal is sent on GPRS there is a random access attempt made by the mobile station (MS) being utilised to connect to the network and thereby to a remote WWW server to facilitate the download of a required web page.
Upon the occurrence of a random access attempt, the MS sends a message to the network, via a base transceiver station (BS), that it has data to send. When the MS receives a signal from the network that it may send data, the MS is allocated a number of packets of future time in which to send that data. However, if there are two requests made to the network at the same time, collision of access attempts may occur. In this event, a SYN signal will not be transmitted by the network and the MS must make a further random access attempt later in time. This is known as random access contention resolution.
As will be explained below, the problem that exists is the necessity to establish a radio link control (RLC) link for every TCP/IP session. Radio link control is a protocol which controls the transfer of blocks of information between the MS and network. It performs sequenced delivery and error correction. The need to establish separate radio links increases substantially the delays experienced by the user in downloading a web page and the images contained therein. Delays are further accentuated given that the current form of RLC protocol requires that a countdown procedure is used to close down a link. Such a procedure consists of counting down the remaining number of blocks to be sent from a pre-set number to zero. The shut down of the link occurs upon zero.
The delays that occur during the download of a web page may best be appreciated by referring to FIG. 2, which shows a ladder diagram illustrating the message exchanges involved in the sending of a SYN message from client to server and from server to client. The following general assumptions have been made in the construction of the ladder diagram. It should be stressed that these assumptions are purely exemplary.                1. The major time delays are attributed to temporary block flow (TBF) establishment and wide area network (WAN) and data transfer time, such as satellite delay when making a transatlantic connection, for example.        2. The time overhead for the creation of an uplink TBF is larger than the time overhead for the creation of an uplink TBF whilst the downlink TBF is active.        3. The establishment of a downlink TBF has a time overhead less than that for the establishment of an uplink TBF.        4. Data transfers have an associated block error rate (BLER) of 10%.        5. The RLC roundtrip delay for data transfers is 10 RLC blocks.        6. Data is transferred at the lowest code rate (highest throughput).        
The terminology used within these assumptions will become clearer in the light of the following description relating to FIG. 2.
As may be seen in FIG. 2, the connection between web browser and remote server on a GPRS involves various layers of control which interact with one another to enable communication links to be created. A browser communicates via a transmission control protocol (TCP) layer, which communicates with a logical link control (LLC) layer, which communicates with the mobile station radio link control (RLC-MS) layer. From here, messages are broadcast from MS to BS across a radio link formed therebetween. Messages received at the base station radio link control (RLC-BS) level are communicated to a logical link control/transmission control protocol (LLC/TCP) layer and thereon to the TCP layer of the remote server. Of course, this operates in reverse also.
Referring again to FIG. 2, the browser sends a HTTP request 2 which is sent as a SYN signal 4 by the TCP layer, this signal is sent on as a set synchronise balance mode (SABM) signal 6, by the LLC layer to the RLC-MS layer. At this stage an uplink TBF 10, a connection between MS and BS for the transfer of information in terms of RLC blocks, is established.
After establishment of the uplink, a TCP signal is passed on from the RLC-BS layer to the LLC/TCP layer as a connection indication (Conn-ind) signal 12. An acknowledgement signal 14 is sent back from this layer to the LLC layer which in turn sends an information frame 16, comprising TCP information and a SYN signal, back to the LLC/TCP layer. The next stage involves the sending of a SYN signal 18 from the LLC/TCP layer to the TCP remote server. This then sends a SYN signal 20 back, which is transmitted onwards to the RLC-BS as an SABM signal 22.
Now a downlink TBF-connection for transmittal of RLC blocks from BS to MS is established. This step is generally indicated as 24. After downlink establishment, a connection indication (Conn-ind) signal 26 is sent onwards to the LLC layer. This is acknowledged by acknowledgement signal 28 which passes across the air interface between MS and BS to the LLC/TCP layer. From there an information frame is sent across the radio link and onwards to the browser TCP layer.
Here it is assumed that the downlink TBF is closed after polling using the related reserved block period (RRBP). A BS may send a message with the RRBP set so that the MS must respond with an acknowledgement signal at the RLC level within a certain number of RLC blocks. If the RRBP does not require that the downlink remain open for such an acknowledgement, the downlink will be closed.
It is clear to see that these two signals, the first two depicted in FIG. 1, have taken a specific time (τ) to be passed. Such a connection must be made a number of times in any one web page download operation. There is thus a problem in that the requirements for downloading web pages using HTTP on a GPRS can be very high. The stated problem becomes more significant when exemplified with regard to time periods. For the download of a single web page containing no images, three connection and tear down sequences must be carried out. One to establish that data is required, one to notify the server of what data is required and to receive the data, and a final one to acknowledge. Obviously, this will increase by the duration of a further connection and teardown sequence for every image to be downloaded. The problem requiring a solution is, therefore, how to reduce the time requirements for downloading a web page using sessions or applications protocols which use successive TCP connections within a session on TDMA wireless packet data systems or wireline modem access protocols, thus increasing efficiency and user satisfaction.